N-doped EG@MOFs derived porous carbon composite phase change materials for thermal optimization of Li-ion batteries at low temperature

Electric vehicles often encounter the challenge of battery capacity reduction in cold environments. Existing thermal conductive patches and partial short-circuiting for electrical heating can address the above issues. In this paper, a method to increase battery capacity was proposed by phase change material (PCM) assisted heating. Specifically, a nitrogen-doped hierarchical porous carbon (NPC) was synthesized through a combination of “low-temperature calcination + concentrated nitric acid treatment” to treat the chrysanthemum-shaped MOF-199@EG, and impregnated with stearic acid (SA) to form a stable composite PCM. With its well-developed pore structure and N-adsorbed active sites, the NPC prevents the leakage of molten SA, maintains stability effect and significantly improves the thermal properties of SA composites. The SA/NPC has a loading rate of 80.15 wt%, closely approaching the theoretical values of latent heat (137.89 J·g-1). It also demonstrates enhanced thermal conductivity (1.873 W·m-1·K-1) and thermal diffusivity (1.024 mm2·s-1). Thermal conductivity and thermal diffusivity of SA/NPC are 8.56 times and 14.06 times higher, respectively, than those of SA. Furthermore, when the lithium-ion battery is discharged 2C at −20 °C, the utilization of SA/NPC as an insulation material can increase the discharge energy by 7.89 %. Consequently, this novel composite PCM holds significant promise for the thermal optimization of batteries at low temperature.